The present invention relates to a wire stitching or stapling machine of the type which severs and forms staples from a continuous wire and drives the staples into an associated workpiece. In particular, the invention relates to a stitching head for such a machine.
The present invention is an improvement of the wire stitching machine sold by Interlake, Inc., the assignee of the present invention, under the trademark "CHAMPION STITCHER". This prior stitching machine, which is in turn an improvement of the machine described in U.S. Pat. No. 1,252,011, includes a stitching head having a wire feed mechanism for feeding a predetermined length of wire from a continuous wire supply to a wire holder, where the length of wire is severed from the supply, and a staple-forming and driving mechanism which forms the severed length of wire into a staple and drives it into an associated workpiece. The mechanism undergoes a cyclical reciprocating movement comprising a drive stroke and a return stroke. During each drive stroke the feed means is feeding a predetermined length of wire to the wire holder, while the staple-forming and driving means is forming and driving the length of wire which had been fed during the preceding drive stroke. Both mechanisms then retract simultaneously, and at the end of each cycle there is left in the wire holder a severed length of wire ready to be formed and driven during the next drive stroke.
This type of stitching head operates to form a standard staple which is substantially in the shape of an inverted U, having a pair of parallel leg portions interconnected by a straight bight portion disposed substantially perpendicular to the leg portions. When the staple is driven through the associated workpiece the legs are folded over by a clincher to complete the stapling or stitching operation. In its clinched condition the staple has both its bight portion and its leg portions disposed flat against the associated workpiece.
However, for certain applications it is desirable to provide a staple wherein the bight portion or a part thereof forms a "loop" which is spaced from the associated workpiece. This type of staple is useful in certain applications, such as in the preparation of a loose leaf binder. Thus, pages of the binder can be stapled together and folded, so that the loop portions of the staples can be inserted over the rings or posts of a loose leaf binder. However, such "loop"-type staples cannot be formed on the stitching machine of the type disclosed in the aforementioned U.S. Pat. No. 1,252,011, or in the Interlake "CHAMPION STITCHER".
Such "loop"-type staples and machines for forming them are known, but such machines are of a completely different construction from that of the Interlake "CHAMPION STITCHER". Furthermore, all such machines operate by first forming the "loop" portion of the staple then forming the legs thereof.